Magnetic Properties of Weakly Doped Antiferromagnets

TL;DR

This paper investigates how small doping levels in a two-dimensional antiferromagnet affect its magnetic properties, revealing significant spin wave softening and increased susceptibility, aligning with experimental observations in doped copper oxides.

Contribution

It provides a detailed theoretical analysis of spin excitations and susceptibility in doped antiferromagnets using the t-J model and self-consistent Born approximation, highlighting the impact of hole motion.

Findings

Spin waves are significantly softened with doping.

Shorter-wavelength spin waves become strongly damped.

Spin wave velocity decreases due to hole motion.

Abstract

We study the spin excitations and the transverse susceptibility of a two-dimensional antiferromagnet doped with a small concentration of holes in the t-J model. The motion of holes generates a renormalization of the magnetic properties. The Green's functions are calculated in the self-consistent Born approximation. It is shown that the long-wavelength spin waves are significantly softened and the shorter-wavelength spin waves become strongly damped as the doping increases. The spin wave velocity is reduced by the coherent motion of holes, and not increased as has been claimed elsewhere. The transverse susceptibility is found to increase considerably with doping, also as a result of coherent hole motion. Our results are in agreement with experimental data for the doped copper oxide superconductors.